Posts Tagged LHC

A while ago I made a somewhat whimsical but as accurate as I could manage too-much-infographic comparing many aspects of the International Space Station with the Large Hadron Collider, and jokingly asking which would win in a fight. I’ve given that a bit of an update and put an annotated text version below for those whose pdf readers don’t show annotations. More importantly, since then, I’ve seen the crew of the STS-134 mission to the space station give a talk at CERN, and wanted to ask them which was more awesome, but was in one of the few spots without a microphone, and I don’t speak as loudly as my friend Hugo, who asked a question from right next to me, does. But at a later talk at CERN, I did ask NASA’s Associate Administrator for Human Exploration and Operations, William H. Gerstenmaier. This was his response, which you can find at around 50:45 in the video:

Oh, man. This is a tough question; I don’t know. They’re both unique in their own way, right? Both pretty special research facilities, right? And I think that, again we often talk about, you know, human versus robotic, right, it’s really human all the time, right? Even in a robotic space, the data’s analyzed by a human somewhere, and so, I think again it’s that spirit of exploration that we’re all pushing on. We all want to understand something new, discover something that nobody’s seen before, so at CERN, damn sure, that spirit drives you every day, you’re looking for new things. I see it in your papers: what is this theory? Are we changing physics? It’s the same thing we’re doing. How can I look at a physical phenomenon that occurs in one gravity, remove the one gravity term, and now get a totally different perspective on that same physical phenomenon, that then allows me to advance in a different area. So I think it’s that same passion that drives people. But I don’t know which one’s best.

So there you go. I’ve added this comment to the notes in the TMIGraphic, and also updated data relating to the ISS’s orbit and a few other things, and added a ‘Getting to Orbit’ section, but the best thing is the update to that ‘when to see it’ bubble on the LHC. You can see it at the CERN open days at the end of September. Two full days. The LHC is shut down for upgrades at the moment, so I understand this will be another chance to actually go underground and see it, which probably won’t be possible for a while once it starts running again. And even if you don’t see the LHC or its detectors (there are only so many people that you can get up and down in a lift in two days; 23 000 people out of 53 000 visitors visited the tunnels in one day last time), there are many other things you can see at the open day. I know this because I was at the last one. Maybe I should look through whatever videos I took that day and see if I can make an interesting montage. I know I have footage from various other tours which I should put online.

The pdf version of the ISS vs. LHC comparison has a lot of links and extra notes in the margins detailing where I got the figures from, how I chose the sources, how I found myself gingerly plugging values into a relativistic equation at a demoparty at 1:30a.m, and so on. But I suspect not everyone who looked at the original downloaded the pdf, and those who did might not have been using pdf readers that showed the notes well. Besides that, the infographic is sort of messy (that’s why I call it a too-much-infographic), although I think it does add something to the raw text. So I’ll reproduce all of the text and notes in table format below, show a far-too-small preview of the TMIGraphic version, and encourage you to download the pdf if you like circles and crisscrossing dashed lines and things that can be read while offline.

Sorry if the line spacing is inconsistent in this table; WordPress changes the style for the second and later paragraphs in each cell no matter how I create the paragraph breaks, and it tends to delete newlines, paragraph and break tags if I ever open the page in the visual editor, so the best I can do is put blank lines before the first paragraph in each cell to give that the same style, and then try not to accidentally open the post in the visual editor.

The ISS mass doesn’t include the contents of the station or any spacecraft docked to it. You’ll find different masses around the place depending on what they take into account.The LHC mass is much more than that (calculated from CERN FAQ – LHC the guide: “4700 tonnes of material in each of the eight sectors”.) The 1232 35-tonne dipole magnets alone weigh 43120 tonnes, and there are another 8468 smaller magnets, and many other things. But only 30 tonnes of each of those dipoles is cooled (by 120 tonnes of liquid helium and 10 080 tonnes of liquid nitrogen)

As my friend Rob Lambert (who works on LHCb) says: It's difficult to define the mass of "the LHC", because you'd probably want to weigh the concrete in the tunnel walls […] I think the "cold mass" is the best comparison to make, since that is sort of like the LHC payload. The rest is sort of comparable to the shuttles/boosters used to get the materiel up to the space station, which weighs a lot more than the station itself, of course.

Weight

368 730 000N

(just the cold stuff, ignoring altitude)

at least 3 614 899N
(using the stated mass at 422km altitude, the point of the ISS’s current orbit where it weighs the least)

For the LHC, this is just a simple matter of multiplying the mass above with standard gravity. The exact gravity where the LHC is wouldn’t be exactly that, due to the altitude, the distance below the surface, the mountains, the tides (which the LHC itself is sensitive can detect) and all sorts of other things that I don’t know how to calculate.As for the ISS, you might think the station is weightless, but it’s not; it’s in orbit. There’s still gravity up there, just a bit weaker than on the ground (where the station would weigh about 4 109 084N.) The station’s weight keeps it falling toward the Earth all the time. It’s just moving along fast enough that the Earth curves away beneath it, so it doesn’t get any closer to the ground. Things on the station seem weightless because they’re in free fall.Here’s a website which gives the formulas to calculate the force of gravity between two objects, and will calculate it for you. I used 5.97219e21 metric tons for the weight of the Earth, 419455kg for the weight of the station, and 6800km for the distance between them (the radius of the Earth, plus 422km.) I probably shouldn’t give the result that many significant figures.

Pressure

Inside:
760Torr (1 atm)

Outside:
10-10 — 5×10-8 Torr

For the ISS, this is actually the pressure at 500km; the closest altitude I could find authoritative-enough figures for. Outside the station, closer to Earth’s atmosphere, the value should be toward the high end of this range.I had a lot of trouble finding an answer to this seemingly-simple question; I found figures which varied by a factor of a billion. In fact it only varies by a factor of 20 depending on the space weather.

When I first did this comparison, it was possible to check the inside temperature of the space station in real time here at the bottom right, but the temperature doesn’t show for me any more.The inside temperature of the LHC is the temperature of the cold mass of the magnets, given here.The ‘Outside’ temperature is actually the temperature of the LHCb cavern when the detector is turned off. I assume the LHC tunnel should be about the same temperature.

5.5 trillion degrees is an estimate from this Nature blog post. This CERN page says: When two beams of lead ions collide, they will generate temperatures more than 100 000 times hotter than the heart of the Sun, concentrated within a minuscule space.

from French and Swiss grid (including the base load for the whole site)

Of the LHC total, LHC cryogenics uses 27.5 MW and the LHC experiments use 22 MW. It’s hard to say how much of the rest goes toward LHC-related computing, lighting, coffee-brewing etc, and how much goes to the many other experiments and activities at CERN.

Here’s the source for the LHC depth figures, and an explanation of why it was built underground. I estimated the altitude above sea level going by altitudes in Google Earth at roughly the points where the LHC is deepest and shallowest. I need to find better figures for this.

Orbit Diameter

13 558—13 586km
(on 2 June 2013)

8485m

I used the mean Earth radius of 6371km to calculate the orbit diameter of the ISS, . I guess I should have calculated the diameter at the actual angle the ISS orbits at, but as a maths major I don’t trust my arithmetic.

I got the 2.76TeV figure from the LHC FAQ document (which is very comprehensive and interesting, by the way. I recommend it.) A nucleon is just a proton or neutron. But I couldn’t find the actual speed, so I calculated it using this formula at 1:30a.m. I’m a maths major, so I can’t guarantee its correctness.

Wolfram Alpha can calculate this by itself if you ask it ‘relativistic speed of 2.76 TeV proton’ but the answer is so near to the speed of light that it rounds it off to 1c.

Orbital Period

~92 minutes

88.928µs (11245 orbits per second)
either protons or lead ions at full energy

The ISS data used to be on the real-time tracking page listed previously, and the LHC figures were here. I’m going to need to find new sources for those.

AMS was designed at CERN, and one of those proton beams came from the Super Proton Synchrotron, which also accelerates protons to inject them into the Large Hadron Collider (see also the bottom half of the too-much-infographic.) The AMS control room is also at CERN.For a while the AMS was just across the road from my office. I took a few pictures of it just before it left, with my phone since my camera was broken at the time. One is shown below. The astronauts who installed it gave a talk at CERN a year after the installation, which you can watch online.

The International Space Station’s Facebook page and also the International Cooperation page say 15 nations. NASA’s Human Space Flight FAQ says 16. I went with the higher number, because people from other countries are probably involved anyway. I know that at CERN, it’s usually the countries of the institutions that are counted, when there might be people from many other countries working for those institutions.

The idea for the LHC (sometimes called the Juratron in early papers, after the Jura mountains) had been floating around since 1977 (see this talk by Lyn Evans for a nice history of the LHC) but 1984 was the date of the first conference about it. The idea was officially approved in 1994.

On-site Assembly

1998—2013

1998—2008

Of course, this depends what you count. The LHC date is from the start of civil engineering to the completion of the beam pipe around the entire circuit including the detectors. There was a huge repair effort after the cooling leak in 2008, and there’s work going on right now to upgrade the detectors and get the LHC itself up to the original design energy of 7TeV.

Having a real-life space station occupied continuously for nearly 13 years, and finding out what the universe is made of? Priceless!

For the LHC, the figure of 4.6 billion is given here, but I chose the CERN FAQ/LHC Guide as the reference since it is newer and probably more carefully checked by more people. This was the booklet given out to volunteers at the 2008 open day.

The paper count for ISS is from August 2012; when I checked again in June 2013, the count was 116, but I assume the other papers still exist. In any case, this is only a rough idea of how much science has been done with the help of the ISS. It shouldn’t be taken as a serious estimate of the benefits thereof.

Fiction

Only fictional space stations can destroy a planet with an energy beam.

Only fictional particle accelerators can destroy a planet with their energy beams.

★★★★★
Most awesome man-made thing in Earth orbit. Don’t make me compare it with Mars rovers.

★★★★★
Most awesome man-made thing on Earth.

They’re both unique in their own way, right? Both pretty special research facilities, right? […] I think again it’s that spirit of exploration that we’re all pushing on. We all want to understand something new, discover something that nobody’s seen before, so at CERN, damn sure, that spirit drives you every day, you’re looking for new things. I see it in your papers: what is this theory? Are we changing physics? It’s the same thing we’re doing. How can I look at a physical phenomenon that occurs in one gravity, remove the one gravity term, and now get a totally different perspective on that same physical phenomenon, that then allows me to advance in a different area. So I think it’s that same passion that drives people. But I don’t know which one’s best. — William H. Gerstenmaier at CERN on 6 November 2012

Here is a handy, sometimes whimsical (but always as accurate as I could manage) comparison between two of my favourite scientific endeavours (now version 1.1, with changes detailed in a new post, along with a HTML table version with all the notes visible.) It is too cluttered with information to be a good infographic, so I’m calling it a TMIGraphic. Click on the image for a higher-resolution pdf with links and copious notes. It’s best if you save it and open it in a pdf reader rather than viewing it in your web browser, as the notes didn’t show up in the browser I tried. Click on each information box for the primary or most readable reference, and click the note icons for more explanations, references and interesting links. If you can’t see the note icons in the pdf, or if clicking on them doesn’t do anything, let me know and I’ll try to figure something out; the notes are important.

I’ve wanted to do this for at least three years; I think it started with wondering which was cooler, and immediately answering myself with the relevant temperatures. When I started this round of Writing Cards (and not so much Letters) I thought I’d work on it slowly throughout the year, then finish it when the appropriate cards came up in one of the NASA decks and the CERN deck in the same week. This didn’t work for two reasons: every time I started to work on it slowly (and also, when I first came up with the idea of doing it as an infographic a year or so ago) I got stuck on the vacuum pressure outside the ISS. And even though the week’s CERN card is about LINAC-1, the NASA card seemed like a challenge that I couldn’t resist. Is the International Space Station really the largest, most complex international cooperative science and engineering program ever attempted? Well, I don’t want to choose a favourite. Let’s just say the Large Hadron Collider is the largest, most complex international cooperative science and engineering program on Earth, and the ISS is the largest, most complex international cooperative science and engineering program in space.

This took longer than my usual deadline of a week, but not through procrastination. Also not so that it would be released four years and two days after the first beam went through the LHC, though I’ll use that as an excuse if it helps. Almost every one of those numbers took quite a bit of effort to get right, and you’ll see in the notes in the pdf (that’s the old pdf, corresponding to the TMIGraphic pictured; here‘s the most recent one) that most of them come with various caveats and explanations, because nothing is simple. I’ll have to update some pages in wikipedia after this. I’m certain I still have some things wrong; maybe some obvious things. Please point them out, and I’ll fix them in the next version. Also, feel free to tell me how bad my layout is, iff you have a better suggestion. I know this is not perfect yet and I intend to keep working on it. If you have ideas of information to add, I’d like to hear that too; especially if you have leads on where to get that information. I can provide the original OmniGraffle document if you want to make your own changes, but I’d have to clean it up a bit first; there are a few things that I just made invisible rather than deleting.

The vacuum pressure outside the station gave me the most trouble; I’d hoped it would be a simple equation, or a statistic NASA would publish on their general ISS fact pages, but mainly I just found statements that the pressure inside the LHC beam pipe was the same as at 1000km altitude. For ISS orbit I found values or equations around the place suggesting values that differed by a factor of a billion, and nothing that seemed convincingly more authoritative than the others. Finally, via the Wikipedia page on orders of magnitude of pressure, I found a NASA document with the numbers for 500km, so I used those. It actually varies by a factor of 20. This is still at least 70km higher than the station, so outside the station it’s more likely to be toward the higher end of that range; that is, a less perfect vacuum than inside the LHC beam pipe.

I also had some technical difficulties with the presentation (apart from the clutter and my lack of graphical talent or training.) Firstly, I’m sorry if colour-blind people have trouble distinguishing anything. I wanted to use a colour-blind safe palette, but the paler colours wouldn’t have had enough contrast with white to work with the style I’d chosen. The colours of the information boxes are not essential anyway; they just group them into broad categories and might make it a bit easier for people to find the corresponding information about the ISS or the LHC.

As for finding the corresponding information boxes about the ISS and LHC, it’s really not optimal. There’s a tangled mess of dashed lines connecting them which is really no more functional than background decoration. I thought of making each info box link to the corresponding one on the other diagram, but although that worked in OmniGraffle, in a pdf viewer it did not zoom in enough on the linked box to make it sufficiently obvious which one you’d just jumped to. I also would have liked to make the links in the notes clickable, and add images to some of them. Again, this was possible in OmniGraffle but not in pdf. I’m not sure if there’s a common format that allows all these things.

So, after all that, the important question: Which one would win in a fight?

Of course it depends what the fight is, and here’s where you can get creative. In a weight-loss competition such as The Biggest Loser, I think the ISS would win, having lost about an eighth of its weight by going up to 426km altitude. Though the LHC did lose a fair bit of helium at one point. Meanwhile, the ISS literally runs rings around the LHC, and would certainly win the high jump. If you have an idea, feel free to comment here or, as the TMIgraphic says, tweet it with the #ISSvsLHC hashtag. Maybe it’ll catch on.

As for the ultimate winner, I’ll let Wil Wheaton have the last word. Science. SCIENCE!

Update: I heard back from my friend who had information on the LHC tunnel temperature (actually the temperature of the LHCb cavern, but it should be about the same), and updated that. I also added information in the notes about the exhibition on the AMS detector which you can come see at CERN Microcosm at the moment, and nudged a few things inwards so the preview is a little narrower. If you’ve gone through all the notes in the old pdf you might already have seen this talk given at CERN by the astronauts who installed the AMS on the International Space Station. I was there, and I wanted to ask (for the purposes of this comparison) which they thought was the most awesome out of the LHC and the ISS, but I was in one of the few spots without a microphone.

One thing I’d been meaning to mention is that the path to ‘orbit’ of both things starts with a proton and continues with a booster. The first module of the ISS was put into orbit using a Proton rocket, and many of the rest were taken to orbit on the space shuttle, with its solid rocket boosters. In the LHC, it’s the particle called a proton and the Proton Synchrotron Booster which accelerates it as part of the journey to the LHC.

An oddly powerful number of people liked this when I posted it on facebook, so I may as well put it here as well.

I have a few other things I will put on this blog once I get time, including the source file for the MacinTalk Still Alive, since somebody asked for it, but this will do for now. I’m also testing out the link between Twitter and WordPress, because I got tired of only twittering about goats.

Note: I wrote this with the tune and sentiment of Tom Smith‘s A Boy and his Frog (mp3) in my head. If you know the tune, please imagine that this poem is sung to the same tune as whichever verses it fits.

You might think that we’re just doing science
With a hadron collider so large.
But we’ve built this electric alliance
to give weight to our positive charge.

Take researchers from every nation,
Let the humans within them collide.
We will find the grand unification
when we see we’re all on the same side.

And with ev’ry race, tongue and religion
we’ll find how to give all the world mass.
If we’d all interact just a smidgen
with the openness through which we pass

we’d see life’s ups and downs become charming and strange,
when we face them head on, and what’s more,
seeking beauty and truth we can make a big change
with small change from the purses of war.

Take the light at the end of the tunnel,
and ensure it goes all the way round,
to illuminate more than the sun’ll,
and enlighten with what we have found:

When you’ve unresolved matters, and not enough kin,
and face too many forces to name,
if you cut out the din, and put energy in,
it turns out that we’re all just the same.

This is to be sung to the tune of ‘Still Alive‘ by Jonathan Coulton. I will post a recording, and probably a video, some time in the next few days.

This isn’t TRIUMF
We’re sending a beam through CMS.
Can’t wait to see some novel interactions.

Popular Science
will call up their troubadour(k)y man
To sing in praise of all of us
and he’ll sound better than this.

But there’s no sense cheering over every beam
they’ll just keep appearing till you have an umpteen
when the celebration’s done,
do your calibration run.
Tell the crackpots they’re all still alive.

We’re not yet colliding.
But soon we’ll be lighting up the barrel
with 14 TeV of former protons
We’ll smash them to pieces
and slam every piece into a wire
except the LSP because
it will go all the way through.
Now our points of data come from crystals of lead tungstate,
and we’re out of beta we’re releasing a few years late
but the science gets done,
and more funding will come
now you’ve seen that you’re all still alive.

We’ll find the Higgs boson.
We’ll find that the answer’s forty-two.
Maybe we can even find the question.
We’ll blow up the planet.
That was a joke. ha ha, fat chance.
Anyway, this spaceplane’s great,
let’s try to make it collide.
Look at me still talking when there’s science to do
when I look up there I think I see a mu-mu.
But we need to repair
see you in the new year,
In the meantime the DAQ’s still online.

And believe me we are still online.
We’re taking cosmics and we’re still online
And when there’s beam we will be still online
And ISOLDE will be still online
Because those show-offs had beam all the time.
All the time
still online

Between March 21 and 27, 1984, theorists, experimentalists, accelerator physicists, and experts in superconducting magnets gathered for a workshop in Lausanne and Geneva. They were not there to discuss the Large Electron Positron collider, for which excavation of a 27km near-circular tunnel would soon begin at CERN, the European Organization for Nuclear Research. They had come to discuss a possible playmate for the LEP, a collider of protons and perhaps antiprotons to be installed alongside the LEP in the same tunnel. Some nicknamed it the Juratron, after the Jura mountains under which part of it would pass. Officially, it was known as the Large Hadron Collider, or LHC.

The LHC would accelerate protons to an energy of up to 9 TeV, more than nine million times the energy of a proton at rest. To keep such high energy particles on course in a ring as small as the LEP, the LHC would need superconducting magnets with a magnetic field of 10 Tesla, about 2000 times the strength of a refrigerator magnet (pictured.) The superconductor technology available at the time could theoretically be extended to create magnetic fields of up to 6 or 7 Tesla, but substantial new developments would be necessary to reach the required 10 Tesla.

Carlo Rubbia concluded the workshop with the statement, “Perhaps the time has come for us to pause, at least until the magnet, accelerator, and detector issues have made some significant progress.” There would be no playmate for LEP just yet, but it would come.

The LEP tunnel was made big enough to fit two accelerators. By the end of 1986, only half a kilometre of it remained to be dug. A preliminary technical study on the possibility of building the LHC on top of the LEP was carried out, and it seemed like a better deal than the alternative proposition of a 1 TeV linear electron-positron collider. With the LHC and LEP together, electron-positron collisions, electron-proton and proton-proton collisions would all be possible, with protons injected by CERN’s existing proton accelerators. Nobody had managed to make strong enough superconducting magnets yet, but there was optimism that it was possible.

In 1987, the first LEP magnet was installed in the newly-completed tunnel, and the first model of an LHC dipole magnet was made. To save space and money, the two opposing proton beams would pass through separate channels within the same magnet. Studies were underway of the possibilty of using either niobium-titanium or niobium-tin for the magnets, or perhaps the recently developed ‘high temperature’ superconductors. The next year, a niobium-titanium superconducting magnet was made which could provide a magnetic field of more than 9 Tesla. It was hoped that the LHC would be able to reach an energy comparable to the 20 TeV of the Superconducting Super Collider being built in Texas.

In the early afternoon of Bastille day 1989, physicists were jublilant to see the evidence of the first beam of positrons sent around the LEP: an unassuming white oval on a blue screen. But for all the eyes fixed on the LEP, more than ever were looking forward to its companion, the LHC.

Many studies were carried out on the feasibility of the superconducting magnets, cryogenics, and civil engineering that would be required. All confirmed that such a machine could indeed be constructed. Two models of LHC dipole magnets in niobium titanium, and one in niobium-tin, both produced fields of around 9.4 Tesla. A cost estimation and construction schedule for the LHC were established: it could be put into service by 1998, while only slightly disturbing the functioning of the LEP.

In 1990, more detailed plans of the LHC were prepared, and delegates from CERN member states proposed the idea to their respective states, expecting a decision by 1992. A timely decision would mean that the LHC could start operations in 1998, as predicted, for a cost comparable to that of the LEP. With 9 metre magnets creating a field of 10 Tesla, it would collide two beams of protons with an energy of up to 7.7 TeV each. Four prototype 1 metre long 10 Tesla dipole magnets were ordered from four different companies. A life-sized prototype was constructed, with a field strength of 7.5 Tesla.

On 20 December, 1991, the CERN council unanimously approved the LHC project. By that time, thousands of hours of on supercomputers had been spent simulating the interactions that would occur in the LHC. The council asked that all technical and financial details be worked out by 1993.

Preparations picked up momentum in 1992. A conference in March on the LHC attracted 600 scientists. In October, the LHC Experiments Committee received letters of intent for three possible LHC experiments: ATLAS (A Toroidal LHC Apparatus), CMS (Compact Muon Solenoid) and L3P (Lepton and Photon Precision Physics.)

Although the required 10 Tesla field had already been achieved, it was considered too difficult to maintain. Therefore the decision was taken to elongate the dipole magnets to 13.5 metres by deplacing other elements. This would increase the time that the protons were exposed to the field, lowering the necessary field strength to 9.5 Tesla.

In 1993, two of the proposed experiments, CMS and ATLAS were approved, along with a new proposition, ALICE (A Large Ion Collider Experiment.) In December 1993, exactly two years after the council’s approval of the LHC, the requested information was presented. Construction could soon begin.

Like this:

Strong: Did you miss the CERN Open Day? I did, in 2004. It wasn’t my last chance.

I planned my visit to CERN far in advance, and found out on my arrival that an open day was planned for a few weeks after my departure.

Thanks to an Englishman arranging a lift, I did manage to get to CERN’s 50th birthday party in Crozet. The speeches were enlightening… I had never realised that humans could make such bizarre sounds. What they were saying in French, I could only guess. My English companion had learnt enough French at school to understand some of it. From him I learnt one of my first words of French: Cernois, a person who works at CERN.

I wrote in my travel log:

After I’d looked at everything, I bought too much stuff at the souvenir shop, just like I did at the Apple Campus. The reason is the same — ‘when am I ever going to be here again?’ and so is the answer to that rhetorical question… when I work there.

A month before writing that, I had found out that my application for a CERN junior fellowship had been rejected. While still in Geneva, I found out that I had not been accepted into CERN’s Marie Curie fellowship programme either. So when I got home, I applied again.

My Marie Curie fellowship began in April 2005 and ended two years later. Before the end of the fellowship, I had been offered a position at ETH Zurich, based at CERN, so I continued going to work as usual, inasmuch as working at the world’s largest scientific facility can be considered usual.

That September, I got wind that CERN would be having open days the following April. I sent the news to everybody I knew, hoping that with enough notice, nobody with the slightest chance of making it to Geneva would miss out as narrowly as I had. I realised that as a Cernoise, I had the once-in-a-lifetime chance of not only going to a CERN open day, but being part of it. So I signed up as a volunteer for the Cernois-only open day on the Saturday.

Weak: I arrived at CERN at 8a.m, and was given a lift to the CMS pit in Cessy by a colleague and fellow volunteer. We all had our official T-shirts, windbreakers, and polar fleeces, several sizes too large. Guides had their hard hats, the people at the info point had their souvenirs to sell, physicists had brains brimming with answers, and I… I had tables, paper, coloured pencils, and pictures of CMS for colouring in. Kids’ corner.

After lunch I found myself alone at the art table, with two children approaching. Their mother asked in French if this was where they would be minded while she went underground, and would I like to take down her phone number? Would I? I had no idea. I looked around, only to have some guides confirm that it was indeed me in charge of the kids’ corner.

I mutely took the number, and finally the mother asked me in English whether I spoke French. Oui, oui, bien sûr… I like to pretend that I do. She explained to her kids that I didn’t. By this time the kids had the idea that I was a little odd, and sat there glumly staring. I asked in French if they wanted to draw something. They didn’t. The older one started halfheartedly colouring in. I tried to bribe them with promises of prizes for good drawing. They did not respond. Not sure of what else to do, I sat and dutifully watched them, feeling like some kind of psychopath. I started drawing, in an attempt to look less like one. Anyone who had seen my drawings would not have been convinced.

To my relief, a friend appeared with his young nephews, and I talked to him for a while, occasionally checking that my charges hadn’t exploded.

When the mother finally came to rescue her children from their ill-adapted babysitter, the younger one, who had barely touched his pencils, didn’t want to go. Perhaps, in the end, I am quite interesting to glumly stare at. I probably would have held the Cernois in awe too, if I’d been a member of the public at the 2004 open day.

Electric: Sunday was the open day for the general public, and the day when I, too, would be in the general public rather than a volunteer.

The bus to CERN was almost full at its first stop. It was great to see that I wasn’t the only one excited about the open day. At CERN, there were already crowds surrounding the Globe of Science and Innovation, near the entry to visit the ATLAS experiment. I’d already seen ATLAS, thanks to a friend who was trained as an ATLAS guide, so I headed into the rest of the site to see what else there was to see.

The whole place was eerily quiet. I saw a few signs, but no crowds to show me what might be interesting. I went to the café in bulding 40, knowing that there should be some events there, or at least some coffee. There were more volunteers than visitors, and no food yet. Still five minutes until the official start of the open day.

The restaurant was not crowded. I bumped into the friend from the day before, with his nephews and the rest of the family. Was it another day for the Cernois, after all? I checked the volunteers’ interface on the web. There was a few hours wait to visit ATLAS. The amateur radio club was still waiting for visitors. Shuttles supposed to take people from the Meyrin site to visit the ALICE experiment had still not arrived. At 9:30, I heard that some friends of mine who had come from Lausanne early that morning had already been underground to see CMS. What was going on?

What was going on was that 20 000 people were going underground to see the LHC and the detectors. 20 000 out of a previously stated maximum limit of 15 000.

The first visitors arrived at CMS at 7a.m. With queues filling the detector assembly hall and stretching hundreds of metres down the street, there was little choice but to start the underground visits half an hour early, at 8:30. The elevators ran at full capacity and full speed. At LHCb, tour sizes were kept smaller in order to allow more foreign language tours, but they still had a huge number of visitors. By 11a.m. the waiting time to see ATLAS was close to four hours.

Meanwhile, the rest of the 53 000 visitors were dispersed around the various sites, watching machines making machines, Nobel prizewinners making revelations, superconducting magnets making people and things fly, superfluids making their way up the walls of their containers, and actors making out they’d lost some protons.

By the end of the day, the forecast cold and rain had finally arrived. My friends drove me the short distance to the bus stop, where a busload of people were already waiting. One had come from London. One from Paris. One was an art student from Lausanne, who was more interested in the logo and other designs used for the event. One was a guide for CMS, who had volunteered to guide people in English and Portuguese, but ended up speaking French all day and getting a sore throat from it. When the bus arrived, the crowd surrounded it like a plague of zombies… but so much more alive.